The present invention relates to a mechanism for agitating the toner in the replenisher of an electrophotographic copier/printer machine and in one of its aspects relates to a replenisher for supplying toner in an electrophotographic machine wherein the replenisher has a specially designed xe2x80x9cbeaterxe2x80x9d element which effectively aerates the toner particles and keeps them in a fluid state so that they readily flow from the replenisher upon demand.
In a typical electrophotographic machine (e.g. copier, duplicator, printer, etc.), a continuous loop of photoconductor film is commonly used to transfer an image from an input section onto a receiving medium (e.g. a sheet of paper or the like). The film is charged and passed through an input section where an image (i.e. analog or digital) is projected onto the charged film. The film then moves through a developing section where toner (i.e. dry ink) is applied to the charged image before the image is transferred to the sheet of paper. The paper is subsequently passed through a fuser section where the toner is fixed to the paper by passing the paper between a pressure roller and a heated roller.
Before applying the toner to the charged image, many electrophotograpic machines mix the toner with a carrier to form a two-component developer. When using two-component developers, it is necessary to maintain a desired ratio of toner to carrier; this ratio being commonly known as xe2x80x9ctoner concentrationxe2x80x9d or xe2x80x9cTCxe2x80x9d. Typically, the TC may range from about 2% to about 14% by mass for general printing applications. However, as will be understood, the actual range of the TC may vary over different ranges depending on the densities and/or relative size of the particular toner and carrier particles being used.
To maintain the proper TC in a particular machine, the toner typically flows from a source (e.g. a bottle or other container) into a mechanism known as a xe2x80x9creplenisherxe2x80x9d which, in turn, feeds the toner to the developer at a desired rate. Since the charge of toner dictates other process settings within the printing/copying machine, it is vital that the replenisher be capable of maintaining a consistent and controllable flow rate of toner to the developer throughout the printing operation.
Unfortunately, however, it is sometimes difficult to maintain a constant flow rate of toner from the replenisher; especially when certain materials have to be added to the toner to alleviate other problems (i.e. xe2x80x9ctoner rub-offxe2x80x9d) which may be encountered during operation. xe2x80x9cToner rub-offxe2x80x9d is an image quality defect that is created when the friction between two sheets of paper causes some of the fused toner on a original sheet to xe2x80x9crub-offxe2x80x9d onto second sheet as the second sheet moves across the original sheet. To alleviate rub-off, certain additives, such as waxes, are added to the toner before they are fed into the replenisher.
In doing this, problems arise in that typical additives which reduce rub-off often increase the cohesiveness between the toner particles to the extent that they sometimes tend to stick to one another. This, in turn, can cause xe2x80x9cbridgingxe2x80x9d within the replenisher and/or the toner source (e.g. bottle) which feeds the replenisher. As will be understood, xe2x80x9cbridgingxe2x80x9d is the phenomenon wherein abutting particles of toner adhere together to form a contiguous mass of toner which, in turn, blocks or inhibits the flow of toner particles past the xe2x80x9cbridgexe2x80x9d. Accordingly, bridging in the replenisher can prevent the necessary free flow of toner through the exit opening(s) in the replenisher thereby adversely affecting the TC needed for the successful operation of the developer.
To help in preventing bridging in the toner source and/or the replenisher, other additives, e.g. silica, powders, etc., are often added to the toner particles to reduce the unwanted cohesiveness therebetween. However, it has been found that in some cases where the cohesiveness between the toner particles has been reduced, the toner then flowed too well. This, in turn, unfortunately increases the packing density or xe2x80x9cvolume fractionxe2x80x9d of the toner (i.e. volume of toner/volume of replenisher). If the volume fraction is increased beyond a set value, the toner becomes packed within the replenisher and often impedes the motion of the agitator element (e.g. oscillating basket, rotating wire or blade elements, etc.) which is provided in the replenisher to keep the toner particles in a fluid state. If the agitator becomes impeded, the ability of the replenisher to furnish fresh toner reliably is greatly compromised. In some known machines, stalling of the agitator mechanism is also likely to stall the associated feed apparatus, e.g. a feed auger, thereby halting all toner replenishment to the developer which, in turn, requires shut-down of the machine.
Accordingly, those skilled in this art will readily appreciate the need for a replenisher, which has the capability to keep the toner in a state of flux as the toner is supplied from a source (e.g. toner bottle) into the developing station of an electrophotographic machine. This will allow the flow rate of the toner particles, hence the TC, to remain substantially constant throughout the operation of the machine thereby maintaining a high quality product throughout the printing operation.
The present invention provides a replenisher for agitating particulate toner to facilitate flow of toner in an electrophotographic apparatus. Basically, the replenisher is comprised of a housing having a sump, which is adapted to receive and store the toner until needed. An agitator element is rotatably mounted within said sump and is adapted to impart both shear and normal forces to the toner as the agitator element is rotated through the toner. This effectively xe2x80x9caeratesxe2x80x9d the toner and keeps it mobile as it is fed to the developing station in the electrophotographic apparatus.
More specifically, the agitator element of the present invention is a beater element having a hub, which is mounted on a shaft, which, in turn, is rotatably mounted in the housing of the replenisher and which extends through the sump.
A plurality of blades extend radially outwardly from the hub wherein all of the blades are designed to impart substantial shear force to the toner in said sump. Some of the blades are designed to impart a substantial normal force along the rotational axis of the beater element while others of the blades are designed to impart substantial normal force to the toner partially towards or away from the axis of rotation when the hub is rotated. The plurality of blades is aligned in first and second sets, each set being comprised of a pair of diametrically-opposed blades extending outwardly from the hub.
The first set(s) of blades are constructed to impart shear force and a normal force in the axial direction to the toner when rotated therethrough and the second set(s) of blades are constructed to impart shear force and a force normal to the rotation plane, towards or away from the axis of rotation, to said toner when rotated therethrough. The outer ends of all of the blades are twisted at a first angle (e.g. about 30xc2x0) with respect to the radial plane of said beater element. However, only the outer ends of the second sets of blades are bent at a second angle (about 45xc2x0) with respect to the respective radial axis of the blade with the ends of the blades in each set of the second sets of blades being bent outward from the radial axis in different directions.
The replenisher also includes means for delivering an impact to the toner in the sump, which is basically the same as found in known replenishers of this type. This means is comprised of a cam, which is affixed onto one end of the shaft on which the beater element is mounted. An impact element comprised of a leaf spring having a weight thereon is mounted on the outside of said housing. The impact element is adapted to be engaged by the cam when said shaft is rotated to thereby push the impact element away from said housing and then release it so that the bias of the leaf spring will cause the weight to deliver an impact to said housing.